As the price of fossil fuels rises, many small businesses and other users of heating devices have turned to less expensive renewable energy alternatives, such as biomass (biofuel)-fired heating equipment. Unfortunately, complete combustion rarely occurs in this type of equipment. Consequently, biomass-fired heating equipment often is a significant source of particulate matter (PM), carbon monoxide (CO) and volatile organic carbons (VOCs).
In addition to carbon dioxide, nitrogen and water that are released by complete combustion of biomass, incomplete combustion produces various inorganic gases, such as carbon monoxide, ozone and nitrogen oxides, as well as polycyclic aromatic hydrocarbons (PAHs), benzene, aldehydes, free radicals and inhalable particulate matter (PM), all of which have been shown to negatively impact human health. While smoke from biomass units is known to contain a number of compounds that are toxic and/or carcinogenic to humans, one of the pollutants of greatest concern is biomass derived particulate matter.
According to United States Environmental Protection Agency (EPA) particulate matter emissions estimates from 2011, biomass combustion products account for about 2.5% of all U.S. national emissions having diameters smaller than about 10 microns (μm) and 8.1% of all U.S. national emissions having diameters smaller than about 2.5 microns. It is important to note, however, that in some communities, biomass combustion's contribution to ambient particulate matter levels is even more significant, with levels as high as about 42-56%. Inasmuch as about 70% of indoor particulate matter comes from outside sources, biomass-derived particulate matter can quickly become an indoor air problem.
Particulate matter begins to effect health when particles smaller than about 10 microns (PM10) are inhaled, as these particles can bypass natural filtration systems present in human noses and respiratory tracts. Particles smaller than about 2.5 microns (PM2.5), and especially particles smaller than about 0.1 microns (PM0.1), are of great concern, because these particles are small enough to enter alveoli of the lungs and travel into the blood stream. While particulate matter itself can do structural damage to lungs, a major concern is other substances, specifically carcinogenic or toxic compounds, that these particles can carry into an individual's lungs and blood stream, including free radicals, hydrocarbons, such as PAHs, benzene and styrene, as well as aldehydes and phenols. Notably, diameters of particulate matter released during biomass fuel combustion peak at about 0.1-0.2 micron, with a majority of all particulate matter less than 1 micron in diameter.
In addition to its toxic and carcinogenic effects, short-term particulate matter exposure can lead to increased heart attacks, increased hospitalizations for cardiovascular disease, increased mortality, decreased lung function and increased hospitalizations for asthma and respiratory causes among children. Long-term exposure to particulate matter has been associated with higher rates of lung cancer, cardiovascular disease and mortality, as well as decreased life expectancy. The state of Washington estimates that US$190 million was spent each year recently on health expenditures due to particulate matter exposure, with national estimates in the billions of dollars. Globally, the World Health Organization (WHO) estimates that particulate matter exposure is responsible for nearly 800,000 premature deaths. It is important to note, however, that these studies looked at particulate matter from all sources, and that the premature deaths, morbidities and associated costs incurred from biomass combustion emissions from commercial sources would be proportional to their contribution to national particulate matter levels.
The EPA currently has national emission regulations in place for biomass fired heating units that have firebox volumes not exceeding 20 cubic feet, air-to-fuel ratios of less than 35:1, burn rates less than 5 kilograms per hour and total unit weights not exceeding 80 kilograms. Unfortunately, many units that are used commercially exceed these size parameters and are, therefore, exempt from these emission standards. In 2007, a voluntary emissions program was implemented by the EPA to begin to regulate these larger commercial heating units. However, as of 2013, only ten states have adopted the suggested emission requirements. While these regulations are voluntary, it is important to note that these emission regulations only apply to newly installed biomass fired heating equipment. They do not apply to a large installed base of existing units.
EPA regulations limit the amount of particulate matter, measured in grams per hour, that may be emitted by biofuel-fired heating devices, such as stoves, furnaces, boilers, kilns, roasters and other devices that are fueled by stick wood, wood pellets, grass pellets, wood chips or other bio-solids. Particulate matter is typically produced due to incomplete combustion of fuel. There is, therefore, a need to improve combustion efficiency. Such improvements in efficiency typically lead to decreases in the amount of particulate matter produced per unit of heat generated and increase the amount of heat generated per unit of fuel consumed.